Safety lighting unit



May 22, 1956 M. T. KENNEDY, JR., ETAL 2,747,078

SAFETY LIGHTING UNIT Filed May 6, 1953 3 Sheets-Sheet 1 INVENTORS l/VEVTT T /[NA/EDYJA.

BY ALEXANDER C E/V 5 wwmm*w ATTORNEY! May 22, 1956 M. T. KENNEDY, JR.,ErAL 2,747,078

SAFETY LIGHTING UNIT Filed May 6. 1953 3 Sheets-Sheet 2 mi IN VEN TOR`MM/f/ 7." Aff/wwwa FIG.3. BY ALU f/PCAUf/v ATTORNEYS May 22, 1956 M. T.KENNEDY, JR., ETAL 2,747,078

SAFETY LIGHTING UNJT 3 Sheets-Sheet I5 Filed May 6, 1953 United StatesPatent O SAFETY LIGHTING UNIT Merritt T. Kennedy, Jr., Port Washington,and Alexander C. Allen, East Setauket, N. Y., assignors to Pyrate Sales,Inc., Bayside, N. Y., a corporation of Nevada Application May e, 1953,serial No. 353,274

3 claims. (ci. 24o-11.3)

The present invention relates to a lighting unit safe for use in a zonewhich may contain an explosive or inflammable atmosphere, such as oil orgasoline tanks, mines, chemical plants, etc.

In zones containing inflammable or explosive materials or atmosphere,the use of a conventional lighting unit, susceptible as it is tosparking, arcing, short-circuiting, overheating or breaking, constitutesa dangerous hazard. in such a lighting unit, the main sources of fireand explosion hazard are the light, the wires and the switch.

The object of the present invention is to provide a new and improvedcomplete portable lighting unit or device with wire connections, whichdevice is safe for use in a fire and/ or explosion-hazardous zone andwhich meets the most rigid requirement of security in this respect.

In accordance with certain features of the invention, the portablelighting device comprises a lighting fixture and a control box therefor.The lighting fixture constitutes a sealed chamber which encloses asource of light, such as an incandescent lamp, and which has a lightpermeable wall section; and the control box comprises a pressure chamberwith an inlet connection for delivering a non-combustible gas thereinto,such as carbon dioxide under pressure, or air under considerablepressure, an automatic switch in the circuit with the lamp andresponsive to the pressure in said pressure chamber and operable intoposition to open the lamp circuit, when the pressure in said pressurechamber drops below a predetermined value, and a junction or terminalstation for the leads of said circuit.

The lighting fixture and the control box are interconnected by aflexible conduit extending between the pressure chamber and thelamp-enclosing chamber and establishing pressure communication betweensaid chambers to maintain the lamp in the latter chamber in an envelopeof incombustible gas under superatrnospheric pressure. This flexibleconduit also serves as a shield for the electric wire connections fromthe junction station to the lamp.

The conduit which connects the lighting fixture with -the control unitor box, is preferably flexible, and may be of any suitable structurethat will withstand pressures from within without leakage of air or gasunder greater pressure than atmospheric pressure. Preferably an inertgas is employed with this safety lighting unit. This improved conduitcarries within it the electrical wiring connections between the controlunit and the light or lamp. This makes a complete connection safe fromexplosions between the lighting fixture and the control unit whereinthere is gas under pressure in the connection and within the lightingfixture and within the control unit.

Heretofore in connections between a lighting unit and a far removedelectrical supply, the ordinary wire cord is used and is subject tohaving its exterior insulating surface cut, scratched or broken byreason of being flexed or moved around and over mechanical or steelstructures,

or the like. With the use of a portable light, these prior connectingcords are soon damaged, cut or broken and consequently a defectivewiring develops. Therefore, this prior type of connecting cord is notacceptable in connecting the control unit to the lighting fixture shownherein, and, therefore, it becomes very desirable to have the wireconnections carried within the preferred type of conduit hereindisclosed. If for any reason the electrical cord or wire connectionswithin the conduit become broken or are defective in any manner,explosion from sparks will not take place as there is the inert gasaround the electrical connecting cord or wiring and the gas pressure isgreater than the surrounding atmospheric pressure. Such a safetysituation is not true when the ordinary wiring connecting cord isemployed between a lamp itself and its electrical supply.

In a desired form of flexible conduit employed herein between thelighting fixture and the control unit or box, it is desirable to employa conduit made of flexible metal, or a satisfactory neoprene material,or a flexible plastic conduit which preferably carries a neoprene coatedelectrical cord, or the conduit may be made of a combination of severalof the noted materials.

By means of the arrangement described, the lighting fixture is free fromswitches or similar control devices, which might spark or otherwiseconstitute a source of danger from fire or explosion, and the lamp,which might also constitute a source of such danger, is protectivelyenveloped in a blanket of inflammable or incombustible gas underpressure. The pressure in the sealed light chamber prevents any of thesurrounding hazardous atmosphere at lower pressure from leaking intosaid chamber, thereby preventing this contaminating atmosphere fromcoming into contact with a fire or explosiongenerating source in saidfixture. If for any reason, the inert gas under pressure in the lightchamber should leak out or escape or the walls of the light fixtureshould break, causing the pressure of the gas in said chamber to fallbelow a safe limit, the switch in the control box will automaticallyopen, thereby opening both lead wires of the circuit of the lamp andrendering at the control box the circuit harmless.

Since the control box is isolated from the lighting fixture, and isattached thereto solely through the flexible connection therebetween,this control box, in operation, can be placed in a safe remote positionwith respect to the lighting fixture and outside of the hazardous zone.The control box of the lighting unit, therefore, does not constitute afire or explosion hazard when so positioned.

Because the sealed flexible conduit containing the wires between thecontrol box and the source of light is maintained under the pressure ofthe inert or incombustible gas, the surrounding hazardous atmosphere isprevented from passing thereinto just as in the case of the lightchamber, thereby eliminating the possibility of an explosion or fire dueto any short-circuiting, arcing, or overheating of these wires.

The pressure gas in the flexible conduit serves not only the purposedescribed but also as a means for preventing the dangerous overheatingof the parts by convection, and the walls of said conduit aid byconduction and radiation, to prevent such overheating.

Various other objects, features and advantages of the invention areapparent from the following particular description and from aninspection of the accompanying drawings, in which Fig. l is a sectionsomewhat diagrammatic, showing one way in which a lighting deviceembodying the present invention may be used;

Fig. 2 is a vertical section through the lighting fixture forming partof the lighting device of the present invention;

Fig. 3 is a detail section of the lichting xture taken along the lines3--3 of Fig. 2 but on a larger scale;

Fig. 4 is a detail section of the lighting fixture taken along the lines4.-4 of Fig. 2 but on a larger scale;

Fig. 5 is a side elevation of the control box forming another part ofthe complete lighting device of the present invention;

Fig. 6 is a section of the control box taken along the lines 6 6 of Fig.5;

Fig. 7 is an end view of the control box shown with the end coverremoved;

Fig. 8 is a section of the control box taken along the lines 8 8 of Fig.6; and

Fig. 9 is a wiring diagram for the electric circuit.

Referring to Fig. l of the drawings, the complete lighting unit ordevice embodying the present invention is of the portable type withoutside wire connections to a source of supply, and comprises a lightingfixture 10, a control box 11., and a flexible conduit connection 12therebetween. The lighting xture 1t) comprises an opaque hood 3 3 (Fig.2) made of safe materials, such as aluminum of desired thicknesscombined with other materials, and having a lower skirt i4 formed withan internal light-retlecting surface l5. The materials should be of thecompatible type, i. e., those that will not create a difference inelectrical potential that would result in sparking. Such materials arealuminum and bronze, for example. Across the lower end of this hood i3is a light permeable wall member 16 in the form of a lens of high impactheat resistant material, such as Pyrex glass, forming with the hood i3 alight chamber 17. This chamber i7 is heremetically sealed by anysuitable means. In the specific form shown, the rim of the skirt 14 hasa seating flange 1S and the lens 16 has an annular edge 2b embraced by asealing gasket 2i and sealably clamped against said seating ange by aring 22 secured to said skirt by studs 23.

Supported in the sealed light chamber i7 is a suitable source 25 ofelectric light shown in the form of a conventional incandescent lamp.This lamp 25 is resiliently supported in the light chamber, and for thatpurpose, the upper part of the hood 13 has a pair of oppositely disposedbosses 26 mounting a socket strap 27 by means of screws 2S. An approvedlamp socket 29 into which the lamp 25 is screwed is shown with a base 30of Bakelite or any other suitable safe material and is resilientlysupported on the strap 27 by means of a socket spring 31 in the form ofa ring. This socket spring 3i is secured at diametrically oppositesections to the strap 27 by two bolts 32 and rigidly secured to thesocket base 30 by means of two bolts 33 quadrantly arranged with respectto the bolts 32 and passing through notches 34 in said socket base. Thisspring 31, being exible and the socket base 3ft being fastened oppositethe two bolts 32, will permit the lamp 25 to oscillate to some extentwhenever the lighting fixture bumps against any object. Thus, there isenough flexibility in the mounting of the lamp to absorb shocks so thatit will not be broken or loosened in its socket even though the xture 10be subject to relatively heavy shocks. Also, with this type of exiblemounting, the danger of defective wiring or looseness of the lamp in itssocket is reduced to a minimum.

The lamp socket base 3b carries two screws 36 serving as binding postsfor two insulated wires 37 and 3S and one of the bolts 23 mounted on thestrap serves as a binding post for an insulated ground wire 4i. Thesewires 37, 33 and 41 lead into the lighting fixture in a manner to bedescribed.

The hood i3 has a pair of external rings 42 on the top serving as ameans for suspending the lighting fixture 10, if desired, or tordirecting the lighting fixture to any part of a zone through a cable orrope tied or otherwise attached thereto.

The control box 11 comprises a pressure chamber housing 50 (Figs. 6 and8) of rectangular cross-section and an explosion-proof housing 51preferably of similar rectangular cross-section, made of safe material,such as aluminum, and connected together by means of bolts 52 passingthrough respective confronting flanges 53 extending outwardly from thehousing. The metal to metal ange engagement constitutes anexplosion-proof joint that is acceptable under the Underwriters code.The pressure chamber housing 50 is formed with a partition 54 dividingsaid housing into two compartment chambers 55 and 56.

The compartment chamber 55 is closed at its outer end by a cover plate57 secured to the housing 50 by studs 58, and the compartment chamber 56is hermetically sealed by a rectangular plate 69, serving as a partitionbetween the latter chamber and a switch chamber 6i defined by theexplosion-proof housing 51. This plate 66 is supported against a ange 62extending inwardly and rectangularly from the inner end of the pressurechamber housing 50, and is secured to said plate by means of studs 63threaded into inserts 64 fitted into holes in said flange. A rectangulargasket 65 between the plate 6l) and the iiange 62 serves to sealhermetically the juncture between said plate and said ange when studs 63are tightened down, so that the chamber S6 is hermetically sealed andcan be maintained under gas pressure, as will be described hereinafter,while the adjoining chamber 61 is not hermetically sealed but isexplosion-proof.

The chamber 56 is maintained under pressure by means of anon-combustible or non-inflammable gas, preferably carbon dioxide. Thegas is introduced into the pressure chamber 56 through a pressure valve66, Figs. 6 and 7, which is mounted on the partition wall 54, and whichmay be of the conventional type employed in automobile or bicycle tires.This valve 66 has its outlet end extending into the pressure chamber 56and its inlet end projecting into the chamber 55'.

To maintain the gas pressure in the chamber 56, below a predeterminedmaximum, there is provided a suitable relief valve 67 mounted in thepartition wall 54 and having its inlet extending into the pressurechamber 56 and its outlet as well as the main body of the valveprojecting into the chamber 55. The chamber 55 is not hermeticallysealed, so that this chamber is maintained under atmospheric pressure,which does not interfere with the relief of excess pressure through therelief valve 67.

The chamber 5S enclosing the main bodies of the inlet pressure valve 66and the relief valve 67 protects these valves against possible breakageor injury. Access to either of these valves 66 or 67 is easily gained byremoval of the cover plate 57.

Connecting into one end of the pressure chamber 56 is one end of theflexible conduit connection 12, the other end of which connects into thelighting xture 10. This connection i2 is long enough to permit thecontrol box 11 to be placed outside of a hazardous location while thelighting fixture 10 is operating in said location,v and comprises asealed tiexible conduit serving not only as a means for establishing andmaintaining pressure gas communication between the pressure chamber 56and the light chamber 17, but also as a cable for the wire connections37, 3S and 41 between the control box l and the lighting Vfixture 1G.The connection 12 for this purpose preferably comprises a cableconnector 76 at one end sealably fitted into the end wall of thepressure chamber 56, a exible armour tubing 7l of any suitableconstruction, preferably as conventional copper and bronze construction,secured at one end to said cable connector and shown formed with aninner pipe 72 crimped for flexibility and an outer protective braidedsheathing 73. The other end of this flexible tubing 71 is secured to atube fitting 74 threaded into a stainless steel insert 7S in the top ofthe hood 13.

When the pressure of the gas in the light chamber 17 of the lightfixture 10. drops below a predetermined safe value, the circuit of thelamp 25 is automatically shut down by the opening of the switch in thepressure chamber in the control box. The mans for accomplishing thisoperation comprises a suitable pressure switch 76 in the chamber 6iresponsive to the pressure of the gas in the chamber S6, and operableinto circuit-closing position when the pressure in the chamber 56 risesabove an operable set limit, and into circuit-opening position when thepressure in said chamber S6 drops below a lower safety limit. Thispressure switch 76 is shown of the conventional snap type havingspring-pressed bellows in a casing '77 and a switch mechanism in acasing 78, operated by the expansion and contraction of said bellowsinto open and closed position. The pressure switch 76 is mounted on themounting plate 6l) with the inlet 79 of the bellows threaded into saidplate for communication with the chamber 56. The outside of the bellowsin the casing 77 is under atmospheric pressure, so that a pressure inthe inside of the bellows corresponding to the pressure increase in thechamber S6, causes the bellows to expand and when the pressure in thechamber 56 rises to a predetermined upper value, the switch mechanism inthe casing 78 snaps closed, assuming that the switch was opened. Anydecrease in the pressure in the inside of the bellows corresponding to adecrease in the pressure in the chamber 56 causes the bellows tocontract, and when this pressure falls to a predetermined lower value,the switch mechanism in the casing 78 snaps open.

The control box T11 serves not only for the functions described, butalso as a junction box for the current Wires 37 and 355 of the iampcircuit and for the ground wire 41. For that purpose, connected to theside Wall of the housing 51 is an explosion-proof portable cordconnector 80, by which insulated wires 37a, 35a and 41a are led into thechamber of said housing through a cable S1 having means for connectionto a current feed and ground outlet. In the chamber 6l, the current feedwires 37a and 38a are connected to two contacts of the pressure switch76, as noted in Eig. 9. Two terminals of the pressure switch 76 havecurrent wires 37b and Stb connected thereto and to the binding posts 82of an explosion-proof connector S3 screwed into the plate 6d, see Fig.8. Also secured to one of these binding posts S2 in the chamber 61 isthe ground wire 41a.

The binding posts 32 in the connector 83 extend into the pressurechamber 56 and the current lines 37 and 38 and the ground line 41 insaid chamber connect into their corresponding binding posts S2. Thecircuit of the lamp 25 thereby extends through the control box 11 andthrough the lighting fixture 19 and is automatically rendered eitheroperative or inoperative by the switch 76 in series with said lamp.

The control box 11 is portable and can be conveniently carried fromplace to place. To that end, the two housings Sf? and Sli haverespective ears 85 to which are pivotally connected the ends of aU-shaped handle 86. The confronting flanges S3 are provided withrecesses 87 to permit the handle d6 to nest compactly therein when notin use.

In the operation of the complete lighting device, this device is firstprepared for use by lilling the pressure chamber 56 and consequently theother spaces and chambers of said device in communication therewith withcarbon dioxide, or air under considerable pressure through the inletpressure valve 66, while the cover plate 57 is removed to permit accessto said inlet valve in the chamber 55. This carbon dioxide is deliveredto the inlet pressure valve 66, as for example from a cartridge, andenough is delivered to cause the relief valve 67 to blow according tothe setting of said relief valve. For example, the relief valve 67 maybe set at 20 p. s. i. so that when the pressure in the chamber 56reaches that value, said valve will automatically open to discharge theexcess carbon dioxide. After the cover plate 57 is restored in position,the lighting device is ready for use.

In any mode of use, the lighting device may be carried to the locationof use, and the lighting fixture 10 positioned in the zone containingthe hazardous atmosphere of explosive or combustible nature, while thecontrol box 11 is set at a safe remote distance from said atmosphere. lnFig. l there is shown, for purposes of illustration, one possible modeof application; although it must be understood that the lighting unit ordevice of the present invention is applicable to other situations wherea hazardous atmosphere does or may exist. In the illustrated use, thelighting fixture 10 is lowered into a tank 9 which contains oil,gasoline or other chemicals of an explosive or combustible nature, orwhich previously contained such materials and still retains some of thedangerous fumes therefrom. While the lighting fixture 10 is lowered intothis hazardous location, the control box 11 through the long flexibleconduit connection 12 is maintained outside this location and away fromany dangerous or highly explosive gases.

Since the pressure in the chamber 56 is initially at a maximum, abovethe closing limit of the pressure switch 76, this switch is closed andthe circuit of the lamp 25 will be closed whenever the cord or cable 81is connected to a suitable outlet or to a source of current and to aground connection, thereby causing the lamp 25 to light up. Thispressure switch 76, for example, may be set to kick into closedposition, when the pressure in the chamber 56 rises above l0 p. s. i.and may be set to kick out into open position when the pressure in saidchamber drops below 7 p. s. i.

Since the chamber 17 containing the lamp 25 is under the pressure of theinert gas, this pressure keeps out any contaminating hazardous gasesfrom leaking into said chamber. Also, since the exible connection 12 isunder the same pressure, the contaminating hazardous gases are also keptout of said connection. Therefore, in case of short-circuits, arcing oroverheating of the lamp 25 or of the wires 37 and 38, no explosion ortire will take place in the presence of the inert carbon dioxide.Moreover, overheating of the parts of the lighting device, due to theheat generated by the incandescent filament of the lamp 25, is not aptto occur, since the heat is dissipated from the vicinity of the lamp 25by convection currents created in the gas in the chamber 17 and in thechamber of the flexible connector 12, by conduction to the metal partsof the chamber 17 and the connector 12 and by radiation from theexternal surfaces presented by said parts.

In case of leakage of the gas from the lighting device to an extentsucient to drop the pressure of said gas to a dangerous point, some ofthe contaminating atmosphere might pass into the chamber 17 of thelighting fixture 10 and into the flexible connector 12, thereby creatinga hazardous condition in the presence of a live circuit. However, thedrop in pressure of the carbon dioxide in the chamber 56 below apredetermined value automatically opens the switch 76 in the control box11, so that the wires 37 and 38 are no longer live wires, and the lamp25 is no longer lit. Under these conditions, any leakage of thecontaminating gases into contact with internal parts of the lightingfixture 1G and the flexible connector 12 will not create a fire orexplosion hazard.

if the pressure of the carbon dioxide in the pressure chamber 56 shouldbe reestablished beyond the upper limits, so that the lighting device isagain safe for use in a hazardous location, then the pressure valve 76will automatically close, thereby closing the circuit of the lamp 25,assuming that the inlet wire connections are plugged into a current feedsource.

In the foregoing description, it will be noted that the inert gas isintroduced through valve 66 into pressure chamber 56 by a suitablemeans, such as a pump, or it may be introduced through a valve pipeleading from a supply, or, if desired, a small bomb containing the gasunder pressure could be screwed in to the valve 66 and be puncturedafter being moved to a predetermined posi- 7 tion in relation to theValve. Other types of bombs could be employed for introducing an inertgas.

It will be noted further from the general description herein that animproved and novel safety device or unit has been provided wherein. theswitching arrangement governing or controlling the lamp 25 is readilylpositioned away from any explosive gases even though the light itself inthe fixture 10 is needed within the area where explosive gases arepresent. Also, it will be noted that the inert gas extends from thecontrol unit to the lighting fixture and surrounds the lamp and anystructures where there would be possibilities of sparks due to bad ordefective electrical connections. This pressure is a pound per squareinch greater than atmosphere pressure into which the lighting fixturemay be inserted or lowered, Thus, any explosive gases would not enterthe fixture or come close to any of the electrical connections, therebymaking it quite impossible to have any explosions due to this improvedapparatuswhen positioned to light the inside of a container or abulkhead or other area which may contain explosive gases.

In addition to the above advantageous features, the structure of theapparatus herein and its division into a fixture, and a controllingunit, and the conduit between them, the strength of the apparatusemployed and the ability to dissipate heat created by the lamp, meetsthe Underwriters requirements. With such an improved Safety lightingunit or device, it now becomes possible to light the inside of acontainer or area in a manner not heretofore possible due to possibleexplosions, and with such an improved light, it is now possible tocomplete the desired cleaning of the interior of the container or areain an eicient manner.

While the invention has been described with particular reference to aspecific embodiment, it is to be understood that it is not to be limitedthereto but is to be construed broadly and restricted solely by thescope of the appended claims.

The invention claimed is:

l. A lighting device safe for use in fire and expiosion hazardouslocations, comprising an electric lighting circuit, a lighting fixturecontaining a light chamber, a control box containing an explosion-proofchamber and a pressure chamber and a pressure responsive switch in saidcircuit located in said explosion-proof chamber and having a pressureresponsive element in communication with said pressure chamber foroperating the switch mechanism forming part of said switch, an inletvalve connecting into said pressure chamber for feeding a charge ofincombustible gas under pressure into said pressure chamber, and arelief valve connecting into said pressure chamber for limiting themaximum pressure of the gas charge in said pressure chamber, saidcircuit including an electric cord having one end connecting into saidexplosion-proof chamber and the other end adapted to be connected to acurrent feed station, and a fiexible conduit extendingy between. saidfixture and said control box to contain the wires for said circuit andestablishing pressure communication between said light chamber and saidpressure chamber, said pressure responsive switch being operable to opensaid circuit automatically when the pressure in said pressure chamberdrops below a predetermined value, said control box comprises a chamberfor housing the major portions of said valves, the latter chamber havinga cover plate removable to permit access to said valves, said pressurechamber being located between said explosion-proof chamber and thechamber housing the maior portions of said valves.

2. A lighting device safe for. use in fire and explosion hazardouslocations, comprising an electric lighting circuit, a lighting fixturecontaining a light chamber, a

control box comprising a pressure chamber housing and an explosion-proofhousing connected end to end, said explosion-proof housing defining apressure switch charnber, said pressure chamber housing having apartition dividing the latter housing into two compartment chambers, oneof which constitutes a pressure chamber and the other a valve chamber,an inlet pressure valve connected into said partition and accessiblefrom said valve chamber to permit a charge of incombustible gas underpressure to be fed into said pressure chamber, a relief valve connectedinto said partition and extending into said Valve chamber to maintainthe pressure in said pressure chamber below a predetermined maximum, aremovable cover plate for said valve chamber, a removable plate servingas a partition between said pressure chamber and said pressure switchchamber and hemeticaliy sealing said pressure chamber from said pressureswitch chamber, a pressure responsive switch in said pressure switchchamber having a pressure responsive element in communication with thepressure in said pressure chamber, a connector secured to saidexplosionproof housing and adapted to lead current wires in said circuitfrom a current feed station to the interior of said pressure switchchamber for connection to said pressure responsive switch, and aconnector secured to said partition plate and having binding posts insaid pressure switch chamber for the current wires of said circuitleading from said pressure responsive switch and having binding posts insaid pressure chamber for the current wires of said circuit leading tosaid lighting fixture, and a fiexible conduit secured at its ends tosaid light chamber and said pressure chamber to establish pressurecommunication between said light chamber and said pressure chamber andserving as a conduit for the current wires of said circuit extendingbetween said pressure chamber and said lighting fixture,

3. in a complete lighting device where part of it is subjected toexplosive gases, the combination of a portable control box capable ofbeing positioned away from explosive gases, a lighting fixture with alamp therein capable of being positioned in a chamber where explosivegases exist, a conduit connecting said control box and said lightingfixture and carrying light supplying means to said lamp, said conduitbeing fiexible and substantially leakproof to any gases and duringoperation having gases under pressure therein, said portable controi boxcomprising a chamber for housing a switch automatically opened butclosable under gas pressure and having an electrical inlet for powersupply lines, said lines being sealed in the conduit ieading into saidcontrol box, said lines leading to the switch and leading to a secondchamber, the lines leading to the second chamber being sealed to preventgases from passing from one chamber to the second chamber, said linespassing from said second chamber to said lighting fixture for lightingsaid lamp, and a third chamber in said control box having a gas inletvalve, and an outlet valve for controlling gas under pressure into saidfirst and said second chambers and for preventing pressures from risingmore than a maximum amount in said first and second chambers.

References Cited in the file of this patent UNITED STATES PATENTS1,765,900 Beckmann lune 24, 1930 2,317,426 Wilson Apr. 27, 19432,517,478 Grifiin Aug. l, 1950 2,574,882 McDowell et al. Nov. 13, 1951FOREIGN PATENTS 27,714 Great Britain of 1912

